Packages formed using RDL-last process

ABSTRACT

A method includes bonding a first device die and a second device die to a substrate, and filling a gap between the first device die and the second device die with a gap-filling material. A top portion of the gap-filling material covers the first device die and the second device die. Vias are formed to penetrate through the top portion of the gap-filling material. The vias are electrically coupled to the first device die and the second device die. The method further includes forming redistribution lines over the gap-filling material using damascene processes, and forming electrical connectors over and electrically coupling to the redistribution lines.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.15/693,950, entitled “Packages Formed Using RDL-Last Process,” and filedSep. 1, 2017, which claims the benefit of the following provisionallyfiled U.S. Patent application: application Ser. No. 62/520,112, filedJun. 15, 2017, and entitled “Packages formed Using RDL-Last Process,”which application is hereby incorporated herein by reference.

BACKGROUND

The packages of integrated circuits are becoming increasing complex,with more device dies packaged in the same package to achieve morefunctions. For example, a package may include a plurality of device diessuch as processors and memory cubes bonded to a same interposer. Theinterposer may be formed based on a semiconductor substrate, withthrough-silicon vias formed in the semiconductor substrate tointerconnect the features formed on the opposite sides of theinterposer. A molding compound encapsulates the device dies therein. Thepackage including the interposer and the device dies are further bondedto a package substrate. In addition, surface mount devices may also bebonded to the substrate. A heat spreader may be attached to the topsurfaces of the device dies in order to dissipate the heat generated inthe device dies. The heat spreader may have a skirt portion fixed ontothe package substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A and 1B through 11 illustrate the cross-sectional views ofintermediate stages in the formation of packages using RedistributionLine (RDL) last process in accordance with some embodiments.

FIGS. 12 and 13 illustrate the cross-sectional views of some packagesformed using RDL-last process in accordance with some embodiments.

FIG. 14 illustrates a dual damascene structure and an Under-Bumpmetallurgy (UBM) in a package in accordance with some embodiments.

FIG. 15 illustrates a process flow for forming a package in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A package formed based on Redistribution Line (RDL) last process and themethod of forming the same are provided in accordance with variousexemplary embodiments. The intermediate stages of forming the packageare illustrated in accordance with some embodiments. Some variations ofsome embodiments are discussed. Throughout the various views andillustrative embodiments, like reference numbers are used to designatelike elements.

FIGS. 1A and 1B through 11 illustrate the cross-sectional views ofintermediate stages in the formation of a package using the RDL-lastprocess in accordance with some embodiments of the present disclosure.The steps shown in FIGS. 1A and 1B through 11 are also reflectedschematically in the process flow 200 shown in FIG. 15.

FIG. 1A illustrates wafer 10. Wafer 10 includes bulk substrate 12, whichmay be a silicon substrate, a glass substrate, or a metal substrate.Wafer 10 may have the shape of a typical semiconductor wafer. Forexample, wafer 10 may have a circular top-view shape, and may have an 8inch diameter, a 12 inch diameter, or the like. When formed of metal,substrate 12 may be formed of copper, aluminum, stainless steel, or thelike. In accordance with some embodiments of the present disclosure,there is no active device (such as transistor and diode) and passivedevices (such as capacitor, inductor, and resistor) formed in wafer 10.Wafer 10 has two functions. First, wafer 10 provides mechanical supportto the structure that will be formed in subsequent steps since thesubsequently bonded device dies are very thin in order to have a goodgap filling. Also, substrate 12 may have high thermal conductivity, andhence wafer 10 may act as a heat spreader.

Dielectric layer 14 may be formed at the surface of substrate 12. Therespective step is illustrated as step 202 in the process flow shown inFIG. 15. Dielectric layer 14 may be formed of silicon oxide, forexample, which may be formed by oxidizing substrate 12 in an oxygencontaining environment. Alternatively, dielectric layer 14 is formed byoxidizing substrate 12 in water steam. In accordance with someembodiments of the present disclosure, dielectric layer 14 is formedthrough the deposition of an oxide such as silicon oxide (which may beformed of tetraethyl orthosilicate (TEOS)), silicon oxynitride, or thelike. In accordance with some embodiments of the present disclosure,bond pads 16 are formed in dielectric layer 14. The respective step isillustrated as step 204 in the process flow shown in FIG. 15. The bottomsurfaces of bond pads 16 may be coplanar with the illustrated bottomsurface of dielectric layer 14 in accordance with some embodiments ofthe present disclosure. In accordance with alternative embodiments ofthe present disclosure, bond pads 16 extend into substrate 12, and theportions of bond pads 16 in substrate 12 are shown using dashed lines toindicate that bond pads 16 may or may not extend into substrate 12.

To form bond pads 16, trenches (shown as filled by bond pads 16) areformed by etching dielectric layer 14 and substrate 12, so that thetrenches also extend into dielectric layer 14 and substrate 12. Depth D1of the portions of the trenches inside substrate 12 may be greater thanabout 1 μm, and may be between about 2 μm and about 20 μm, depending onthe thickness of substrate 12. For example, depth D1 may be betweenabout 20 percent and about 60 percent of the thickness of substrate 12.It is appreciated that the values recited throughout the description areexamples, and may be changed to different values.

The trenches are then filled to form bond pads 16, as shown in FIG. 1A.It is appreciated that although features 16 are referred to as bondpads, features 16 may be discrete pads or interconnected metal lines. Inaccordance with some embodiments, bond pads 16 are formed of copper orother metals suitable for hybrid bonding (due to relatively easiness indiffusing). After the filling, a planarization is performed to planarizethe top surfaces of bond pads 16 with the top surface of dielectriclayer 14. The planarization may include a Chemical Mechanical Polish(CMP) process or a mechanical grinding process.

The trenches (and the resulting bond pads 16) may be distributed invarious patterns. For example, the trenches may be formed as discreteopenings, which may be allocated as an array, a pattern of beehive, orother repeat patterns. The top-view shapes of the trenches may berectangles, squares, circles, hexagons, or the like. In accordance withalternative embodiments of the present disclosure, the trenches, whenviewed in the top view of the structure shown in FIG. 1A, may beparallel trenches that extend in a single direction. The trenches mayalso be interconnected to form a grid. The grid may include a firstplurality of trenches parallel to each other and evenly or unevenlyspaced, and a second plurality of trenches parallel to each other andevenly or unevenly spaced. The first plurality of trenches and thesecond plurality of trenches intercept with each other to form the grid,and the first plurality of trenches and the second plurality of trenchesmay or may not be perpendicular to each other in the top view.

In accordance with alternative embodiments of the present disclosure, nometal bond pads are formed in dielectric layer 14 and substrate 12.Accordingly, substrate 12 is a blank substrate formed of a homogenousmaterial (a semiconductor, glass, or a metal), and dielectric layer 14is a blanket planar layer, as shown in FIG. 1B.

In accordance with some embodiments of the present disclosure,micro-trenches 18 are formed in substrate 12. Micro-trenches 18 arevoids in which a coolant such as oil, water, gas, or the like can flowtherein. The formation of micro-trenches 18 may include etching a firstsubstrate (such as substrate 12A in FIG. 1A) to form micro-trenches, andcovering the micro-trenches with another substrate (such as substrate12B) to seal the micro-trenches, wherein openings 15 are formed insubstrate 12B to connect to micro-trenches 18. Micro-trenches 18 areillustrated using dashed lines to indicate they may or may not beformed.

Referring to FIG. 2, package components 20A and 20B are bonded to wafer10. The respective step is illustrated as step 206 in the process flowshown in FIG. 15. Package components 20A and 20B may be device dies orpackages. In accordance with some embodiments of the present disclosure,package components 20A and 20B include one or more logic die, which maybe selected from a Central Processing Unit (CPU) die, a Micro ControlUnit (MCU) die, an input-output (IO) die, a BaseBand (BB) die, or anApplication processor (AP) die. Package components 20A and 20B may alsoinclude one or more memory die. In subsequent discussion, packagecomponents 20A and 20B are referred to as device dies as an example,while they can be other types of devices such as packages, die stacks,memory cubes, or the like. Also, although package components 20A and 20Bare illustrated as having the same structure, they may have differentcircuits, different sizes, different thicknesses, and/or may includedifferent number of device dies therein.

Device dies 20A and 20B include semiconductor substrates 22A and 22B,respectively, which may be silicon substrates. Also, device dies 20A and20B may include interconnect structures 24A and 24B, respectively, forconnecting to the active devices and passive devices in device dies 20Aand 20B. Interconnect structures 24A and 24B include metal lines andvias (not shown). Furthermore, the dielectric layers, in which the metallines and vias of interconnect structures 24A and 24B are formed, may beformed using low-k dielectric materials having dielectric constants(k-values) lower than about 3.0, lower than about 2.5, or even lower.The dielectric material may be formed of Black Diamond (a registeredtrademark of Applied Materials), a carbon-containing low-k dielectricmaterial, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane (MSQ), orthe like. In accordance with alternative embodiments of the presentdisclosure, the dielectric layers in interconnect structures 24A and 24Bare formed of an oxide based dielectric material such as silicon oxideor silicon oxynitride.

Interconnect structures 24A and 24B include metal pads 25A and 25B,respectively, which are in the top metal layer of the interconnectstructures. Passivation layers 28A and 28B (alternatively referred to aspassivation-1) may be formed overlying interconnect structures 24A and24B, respectively. In accordance with some embodiments of the presentdisclosure, passivation layers 28A and 28B are formed of inorganicdielectric materials such as silicon oxide or silicon nitride, and mayhave a single-layer structure or a composite structure. The compositestructure may include, for example, a silicon oxide layer and a siliconnitride layer over the silicon oxide layer. Metal pads 32A and 32B areformed over passivation layers 28A and 28B, respectively, and areconnected to the underlying devices through vias 26A and 26B, which areformed in passivation layers 28A and 28B, respectively.

In accordance with some embodiments of the present disclosure, metalpads 32A and 32B are formed of aluminum or aluminum copper, and henceare sometimes referred to as aluminum pads. Over metal pads 32A and 32B,passivation layers 30A and 30B (alternatively referred to aspassivation-2) are formed, which may be formed using materials selectedfrom the same candidate materials for forming passivation layers 28A and28B.

Device die 20A may include bond pads 34 and dielectric layer 36A at theillustrated bottom surface of device die 20A. The illustrated bottomsurfaces of bond pads 34 are coplanar with the illustrated bottomsurface of dielectric layer 36A. Device die 20B includes bond pads 34and dielectric layer 36B at the illustrated bottom surface. Theillustrated bottom surfaces of bond pads 34 are coplanar with theillustrated bottom surface of dielectric layer 36B. The formationprocess of dielectric layers 36A/36B and bond pads 34 may be similar tothe formation of dielectric layer 14 and bond pads 16, respectively.Dielectric layers 36A and 36B may be formed of silicon oxide or otheroxygen-containing dielectric materials such as silicon oxynitride, forexample. The pattern and the horizontal sizes of bond pads 36A and 36Bmay be the same as or similar to that of the respective bond pads 16, towhich bond pads 36A and 36B are bonded. Advantageously, bond pads 34, bycontacting (and even inserted into) substrates 22A and 22B, provide agood thermal dissipating path, so that the heat generated in device dies20A and 20B can easily dissipate into bulk substrate 12 through bondpads 16.

Device dies 20A and 20B are thin dies, for example, with thicknessesbetween about 15 μm and about 30 μm. With device dies 20A and 20B beingthin, the aspect ratio of gap 38 between neighboring device dies 20A and20B are kept low in order to achieve good gap filling. Otherwise, thegap filling is difficult due to the otherwise high aspect ratio.

The bonding of device dies 20A and 20B to the underlying structure maybe achieved through hybrid bonding. For example, bond pads 34 are bondedto bond pads 16 through metal-to-metal direct bonding. In accordancewith some embodiments of the present disclosure, the metal-to-metaldirect bonding is copper-to-copper direct bonding. Furthermore,dielectric layers 36A and 36B are bonded to dielectric layer 14, forexample, with Si—O—Si bonds. The hybrid bonding may include apre-bonding followed by an anneal, so that the metals in bond pads 34inter-diffuse with the metals in the respective underlying bond pads 16to form metal-to-metal direct bonding.

In accordance with alternative embodiments, as shown in FIG. 1B, no bondpads are formed in wafer 10. Accordingly, the bond pads 36A and 36B asshown in FIG. 2 are also not formed, and the bonding of device dies 20Aand 20B to dielectric layer 14 is through fusion bonding(dielectric-to-dielectric bonding).

In accordance with alternative embodiments of the present disclosure,substrate 12 is a glass substrate or a metal substrate. Accordingly,layer 14 may be formed of a Thermal Interface Material (TIM), which isan adhesive having a high thermal conductivity. Device dies 20A and 20Bare thus adhered to substrate 12 through TIM 14 (refer to FIG. 12). Inaccordance with these embodiments, dielectric layers 36A and 36B in FIG.1 may not be formed, and bond pads 34 may or may not be formed.

Next, gaps 38 are filled by gap-filling material 40, as shown in FIG. 3.The respective step is illustrated as step 208 in the process flow shownin FIG. 15. In accordance with some embodiments of the presentdisclosure, gap-filling material 40 includes an inorganic dielectric,which may be an oxide-based dielectric such as silicon oxide. Forexample, the silicon oxide may be formed of TEOS. The formation methodmay include Chemical Vapor Deposition (CVD), High-Density PlasmaChemical Vapor Deposition (HDPCVD), or the like. In accordance with someembodiments of the present disclosure, gap-filling material 40 is anon-polymer material, which does not comprise polymers such aspolybenzoxazole (PBO), polyimide, benzocyclobutene (BCB), or the like.The polymers have significantly different Coefficient of ThermalExpansion (CTE) than device dies, and will cause warpage of theresulting package and the difficulty in the formation of subsequentfine-pitch RDLs.

A planarization step is then performed to remove excess portions ofgap-filling material 40, so that the top surface of gap-filling material40 becomes planar. A top layer of gap-filling material 40 is leftdirectly over device dies 20A and 20B. In the resulting structure,gap-filling material 40 may be in contact with the top surface ofdielectric layer 14, and encircles each of device dies 20A and 20B.Furthermore, gap-filling material 40 may be in contact with the topsurface of passivation layers 30A and 30B.

In accordance with some embodiments of the present disclosure, there isno polymer layer (such as polyimide, PBO, BCB, molding compound,underfill, molding underfill, etc.) in the structure shown in FIG. 3.For example, device dies 20A and 20B are free from polymer layers, andthe underlying wafer 10 is also free from polymer. Accordingly, thestructure shown in FIG. 3 is free from the CTE mismatch problem, whichis resulted due to the difference between the significant differencebetween the polymers and silicon/silicon oxide, etc. It is thus feasibleto form fine-pitch RDLs over the structure shown in FIG. 3 using theprocesses (such as damascene processes) and materials (such as copperand/or low-k dielectric) for forming interconnect structures in devicewafers.

Referring to FIG. 4, gap-filling material 40 and passivation layers 30Aand 30B are etched to form via openings 42. In accordance with someembodiments of the present disclosure, metal pads 32A and 32B areexposed to via openings 42. In accordance with alternative embodimentsof the present disclosure, some or all of via openings 42 furtherpenetrate through passivation layer 28A and/or 28B, so that some topmetal pads 25A and/or 25B are exposed to via openings 42. In accordancewith yet alternative embodiments of the present disclosure, top metalpads 25A and/or 25B are exposed to some of via openings 42, while metalpads 32A and/or 32B are exposed to some other via openings 42. Thetop-view shapes of via openings 42 may be, and are not limited to,rectangles, circles, hexagons, or the like.

Next, via openings 42 are filled with a conductive material(s) to formvias 44, and the resulting structure is shown in FIG. 5. The respectivestep is illustrated as step 210 in the process flow shown in FIG. 15. Inaccordance with some embodiments of the present disclosure, vias 44 areformed of a homogenous conductive material, which may be a metal or ametal alloy including copper, aluminum, tungsten, or the like. Inaccordance with alternative embodiments of the present disclosure, vias44 have a composite structure including a conductive barrier layerformed of titanium, titanium nitride, tantalum, tantalum nitride, or thelike, and a metal-containing material (such as copper or a copper alloy)over the conductive barrier layer. In accordance with some embodimentsof the present disclosure, a dielectric isolation layer is formed toencircle each of vias 44. In accordance with alternative embodiments, nodielectric isolation layers are formed to encircle vias 44, and vias 44are in physical contact with gap-filling material 40. The formation ofvias 44 also include depositing the conductive material into viaopenings 42 (FIG. 4), and performing a planarization to remove excessportions of the deposited material over gap-filling material 40.

It is appreciated that metal pads 32A and 32B may be used for testing(probing) purpose when device dies 20A and 20B are manufactured. Inaccordance with some embodiments of the present disclosure, some metalpads 32A and 32B may no longer be used after the testing, and hencethere may not be any via 44 over and contacting the respective metalpads 32A and/or 32B. Top metal pads 25A and/or 25B are instead used forconnecting to the overlying structures in accordance with theseembodiments. In accordance with alternative embodiments, some or all ofmetal pads 32A and 32B are used for both testing and signal connection,and hence vias 44 are formed to connect to them, as shown in FIG. 5.Vias 44 may also include some vias 44 connected to metal pads 32A and/or32B, and other vias 44 connected to top metal pads 25A and/or 25B.

FIGS. 6, 7, and 8 illustrate exemplary processes for forming fine-pitchRDLs. The respective step is illustrated as step 212 in the process flowshown in FIG. 15. Referring to FIG. 6, dielectric layers 50A and 54A andetch stop layer 52A are formed. Dielectric layers 50A and 54A may beformed of silicon oxide, silicon oxynitride, silicon nitride, or thelike, or low-k dielectric materials having k values lower than about3.0. The low-k dielectric materials may include Black Diamond (aregistered trademark of Applied Materials), a carbon-containing low-kdielectric material, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane(MSQ), or the like. Etch stop layer 52A is formed of a material having ahigh etching selectivity relative to dielectric layers 50A and 54A, andmay be formed of silicon carbide, silicon carbo-nitride, etc. Inaccordance with alternative embodiments, etch stop layer 52A is notformed. Accordingly, etch stop layer 52A is illustrated using dashedlines to indicate it may or may not be formed.

Fine-pitch RDLs 56A are formed in dielectric layers 52A and 54A forrouting. Since the fine-pitch RDLs in accordance with some embodimentsof the present disclosure are formed using damascene processes, it canbe formed very thin (narrow in a top view) with fine pitches (viewedfrom the top of the structure) smaller than, for example, 0.8 μm. Inaccordance with some embodiments, fine-pitch RDLs 56A are formed using adual damascene process, which includes etching dielectric layer 54A toform trenches, and etching dielectric layers 50A and 52A to form viaopenings. The trenches and via openings are then simultaneously filledwith conductive material(s). A planarization step such as CMP ormechanical grinding is then performed to remove the portions of theconductive material over dielectric layer 54A.

FIG. 14 illustrates a amplified view of an exemplary structure of one offine-pitch RDLs 56A, which includes metal line 56A1 and via 56A2underlying and connected to metal line 56A1. Metal line 56A1 and via56A2 in combination include diffusion barrier layer 46, and metallicmaterial 48 over diffusion barrier layer 46. In accordance with someembodiments of the present disclosure, diffusion barrier layer 46 isformed of titanium, titanium nitride, tantalum, or tantalum nitride.Metallic material 48 may be formed of copper or a copper alloy. Due tothe dual damascene structure, diffusion barrier layer 46 continuouslyextends into metal line 56A1 and via 56A2.

FIG. 7 illustrates the formation of dielectric layers 50B and 54B andetch stop layer 52B. The materials of dielectric layers 50B and 54B maybe selected from the same candidate materials for forming dielectriclayers 50A and 54A, and the material of etch stop layer 52B may beselected from the same candidate materials for forming etch stop layer52A.

Fine-pitch RDLs 56B are also formed in dielectric layers 50B, 52B, and54B. Fine-pitch RDLs 56B include metal lines formed in dielectric layers54B and vias formed in dielectric layers 50B and 52B. The formation mayinclude a dual damascene process, which include forming trenches indielectric layer 54B and via openings in dielectric layers 50B and 52B,filling a conductive material(s), and then performing a planarizationsuch as mechanical grinding or CMP. Similarly, fine-pitch RDLs 56B maybe formed of a composite material including a diffusion barrier layerand a copper-containing material over the diffusion barrier layer,similar to what is shown in FIG. 14.

FIG. 8 illustrates the formation of dielectric layers 50C and 54C, etchstop layer 52C, and fine-pitch RDLs 56C. The formation method and thematerials may be similar to the underlying respective layers, and henceare not repeated herein. Also, etch stop layers 52A, 52B, and 52C may beomitted in accordance with some embodiments, and the correspondingetching for forming trenches may be performed using a time-mode tocontrol the depths of the trenches. It is appreciated that there may bemore dielectric layers and metal layers formed for fine-pitch RDLs. Inaddition, even if some or all of etch stop layers 52A, 52B, and 52C maybe skipped, since the dielectric layers in which the fine-pitch RDLs arelocated are formed in different processes, there may be distinguishableinterfaces between the dielectric layers for forming fine-pitch RDLs56A, 56B, and 56C, regardless of whether these dielectric layers areformed of the same dielectric material or different dielectricmaterials. In subsequent paragraphs, dielectric layers 50A, 52A, 54A,50B, 52B, 54B, 50C, 52C, and 54C are collectively and individuallyreferred to as dielectric layers 58 for the simplicity inidentification. Fine-pitch RDLs 56A, 56B, and 56C are also collectivelyand individually referred to as fine-pitch RDLs 56. RDLs 56B and 56C mayhave similar dual damascene structures as RDL 56A shown in FIG. 14.

Fine-pitch RDLs 56A, 56B, and 56C electrically interconnect device dies20A and 20B. Since the pitches of fine-pitch RDLs 56A, 56B, and 56C arevery small, more fine-pitch RDLs 56A, 56B, and 56C may be formed as theinterconnection between device dies 20A and 20B. This significantlyimproves the density of the fine-pitch RDLs and the routing ability.

FIGS. 9 and 10 illustrate the formation of passivation layers and RDLs.The respective step is illustrated as step 214 in the process flow shownin FIG. 15. Referring to FIG. 9, passivation layer 60 (sometimesreferred to as passivation-1) is formed over dielectric layers 58,wherein vias 64 are formed in passivation layer 60 to electricallyconnect fine-pitch RDLs 56C to the overlying metal pads.

Referring to FIG. 10, metal pads 62 are formed over passivation layer60, and are electrically coupled to fine-pitch RDLs 56C through vias 64in passivation layer 60. Metal pads 62 may be aluminum pads oraluminum-copper pads, and other metallic materials may be used.

As also shown in FIG. 10, passivation layer 66 (sometimes referred to aspassivation-2) is formed over passivation layer 60. Each of passivationlayers 60 and 66 may be a single layer or a composite layer, and may beformed of a non-porous material. In accordance with some embodiments ofthe present disclosure, one or both of passivation layers 60 and 66 is acomposite layer including a silicon oxide layer (not shown separately),and a silicon nitride layer (not shown separately) over the siliconoxide layer. Passivation layers 60 and 66 may also be formed of othernon-porous dielectric materials such as Un-doped Silicate Glass (USG),silicon oxynitride, and/or the like.

Next, as shown in FIG. 11, passivation layer 66 is patterned, so thatsome portions of passivation layer 66 cover the edge portions of metalpads 62, and central portions of metal pads 62 are exposed through theopenings in passivation layer 66. Under-bump metallurgies (UBMs) 68 areformed, and UBMs 68 extend into passivation layer 66. The respectivestep is illustrated as step 216 in the process flow shown in FIG. 15.UBMs 68 may be in contact with metal pads 62. In accordance with someembodiments of the present disclosure, each of UBMs 68 includes abarrier layer (not shown) and a seed layer (not shown) over the barrierlayer. The barrier layer may be a titanium layer, a titanium nitridelayer, a tantalum layer, a tantalum nitride layer, or a layer formed ofa titanium alloy or a tantalum alloy. The materials of the seed layermay include copper or a copper alloy. Other metals such as silver, gold,aluminum, palladium, nickel, nickel alloys, tungsten alloys, chromium,chromium alloys, and combinations thereof may also be included in UBMs68. In accordance with some embodiments of the present disclosure, UBMs68 are formed using Physical Vapor Deposition (PVD) or other applicablemethods.

As also shown in FIG. 11, electrical connectors 74 are formed. Therespective step is illustrated as step 218 in the process flow shown inFIG. 15. An exemplary forming process for forming UBMs 68 and electricalconnectors 74 includes depositing a blanket UBM layer, forming andpatterning a mask (which may be a photo resist, not shown), withportions of the blanket UBM layer being exposed through the opening inthe mask. After the formation of UBMs 68, the illustrated package isplaced into a plating solution (not shown), and a plating step isperformed to form electrical connectors 74 on UBMs 68. The plating maybe an electro-plating, an electroless-plating, an immersion plating, orthe like. In accordance with some exemplary embodiments of the presentdisclosure, electrical connectors 74 include non-solder parts 70, whichare not molten in the subsequent reflow processes. The non-solder parts70 may be formed of copper, and hence are referred to as copper bumps 70hereinafter, although they may be formed of other non-solder materials.Each of electrical connectors 74 may also include cap layer(s) (notshown) selected from a nickel layer, a nickel alloy, a palladium layer,a gold layer, a silver layer, or multi-layers thereof. The cap layer(s)are formed over copper bumps 70. Electrical connectors 74 may furtherinclude solder caps 72, which may be formed of a Sn—Ag alloy, a Sn—Cualloy, a Sn—Ag—Cu alloy, or the like, and may be lead-free orlead-containing. The structure formed in preceding steps is referred toas composite wafer 76.

A die-saw step is performed on composite wafer 76 to separate compositewafer 76 into a plurality of packages 78. Packages 78 are identical toeach other, and each of packages 104 includes both device dies 20A and20B, a piece of substrate 12, and the overlying interconnect structures.

FIG. 12 illustrates package 78 formed in accordance with someembodiments of the present disclosure. These embodiments are similar tothe embodiments shown in FIG. 11, except that bond pads 16 and 34 anddielectric layers 36A/36B (as in FIG. 11) are not formed in theembodiments shown in FIG. 12. In accordance with some embodiments of thepresent disclosure, as shown in FIG. 12, bulk substrate 12, which isalso a blank die, is bonded to dielectric layer 14 through fusionbonding or adhesion. The formation of dielectric layer 14 has beendiscussed referring to FIG. 1B. In accordance with some embodiments ofthe present disclosure, layer 14 is an oxide-based dielectric layer suchas a silicon oxide layer, and the bonding from layer 14 to substrate 12and substrates 22A and 22B may be fusion bonding. In accordance withalternative embodiments of the present disclosure, layer 14 is anadhesive film such as a TIM, which has a high thermal conductivity (forexample, higher than about 1 W/mk), and substrate 12 may be a glasssubstrate or a metal substrate.

FIG. 13 illustrates package 78 formed in accordance with someembodiments of the present disclosure. These embodiments are similar tothe embodiments shown in FIG. 11, except the electrical connectors 74are solder regions (sometimes referred to as C4 bumps). Polymer layersmay be formed to absorb stress. For example, as shown in FIG. 13,polymer layer 80 is formed over passivation layer 66. Polymer layer 80may be formed of polyimide, PBO, BCB, or the like. The formation methodsmay include spin coating, for example. Polymer layer 80 may be dispensedin a flowable form, and then cured. Polymer layer 80 is patterned toexpose the center portions of metal pads 62.

Next, Post-Passivation Interconnects (PPIs) 84 is formed to fill theopenings in polymer layer 80. PPIs 84 are in contact with the topsurfaces of metal pads 62. In accordance with some embodiments of thepresent disclosure, the formation of PPIs 84 includes depositing a seedlayer (not shown), and then plating a metal layer over the seed layer.The seed layer may include a titanium layer and a copper layer (both maybe conformal layers) over the titanium layer. The seed layer may bedeposited using Physical Vapor Deposition (PVD). The plated conductivematerial over the seed layer may include a copper layer, a gold layer,or a copper layer and a gold layer over the copper layer. The platingmay be performed using, for example, Electro-Chemical Plating (ECP) orElectro-less (E-less) plating.

Next, polymer layer 82 is formed to cover PPIs 84. Polymer layer 82 mayalso be formed of polyimide, PBO, BCB, or the like. Next, UBMs 68 areformed, followed by placing solder balls, and then reflowing the solderballs to form solder regions 74.

FIG. 14 illustrates an amplified view of one of RDL 56A (with RDLs 56Band 56C having a similar structure) and one of UBMs 68, which areextracted from FIGS. 11, 12, and 13, with other features in FIGS. 11,12, and 13 are not shown for simplicity. It is observed that bothdiffusion barrier layer 46 and UBM 68 have openings facing the samedirection (facing up in FIG. 14), and the openings face electricalconnectors 74 (FIGS. 11, 12, and 13). Stress is generated when package78 (FIGS. 11, 12, and 13) is bonded to another device such as a devicedie, an interposer, or a package substrate, and the stress propagatefrom the joining point to diffusion barrier layer 46 and UBM 68. Withdiffusion barrier layer 46 and UBM 68 having openings facing the stressgenerating point, diffusion barrier layer 46 and UBM 68 can absorbstress better without passing the stress down to underlying structures.If, however, one of diffusion barrier layer 46 and UBM 68 has itsopening facing away from electrical connectors 74, the stress-absorbingability of the respective one of diffusion barrier layer 46 and UBM 68is degraded.

The package 78 as shown in FIGS. 11, 12, and 13, when having built-inmicro-channels 18, may have pipes (not shown) connected to the oppositeends (such as the illustrated left end and right end), and a coolant maybe conducted into the micro-channels to conduct the heat generated indevice dies 20A and 20B away.

Some exemplary processes and features for three-dimensional (3D)packaging are discussed in accordance with some embodiments of thepresent disclosure. Other features and processes may also be included.For example, testing structures may be included to aid in theverification testing of the 3D packaging or 3DIC devices. The testingstructures may include, for example, test pads formed in aredistribution layer or on a substrate that allows the testing of the 3Dpackaging or 3DIC, the use of probes and/or probe cards, and the like.The verification testing may be performed on intermediate structures aswell as the final structure. Additionally, the structures and methodsdisclosed herein may be used in conjunction with testing methodologiesthat incorporate intermediate verification of known good dies toincrease the yield and decrease costs.

The embodiments of the present disclosure have some advantageousfeatures. By forming the fine-pitch RDLs using the processes typicallyused on silicon wafers (such as damascene processes), the fine-pitchRDLs may be formed to be thin (narrow) enough to provide the capabilityfor the communication of two or more device dies, all through thefine-pitch RDLs. In conventional processes, fine-pitch RDLs were notfeasible using RDL-last process (after device bonding, molding andplanarization). It has been found that the CTE mismatch causes thefin-pitch RDLs, if formed, to break due to the stress. In accordancewith some embodiments of the present disclosure, no polymer or moldingcompound is used underlying the fine-pitch RDL. Instead, oxide-basedmaterials such as silicon oxide are used. This significantly reduces CTEmismatch, and makes the RDL-last process possible. There are also someheat-dissipating mechanisms built in the package for better heatdissipation.

In accordance with some embodiments of the present disclosure, a methodincludes bonding a first device die and a second device die to asubstrate, and filling a gap between the first device die and the seconddevice die with a gap-filling material. A top portion of the gap-fillingmaterial covers the first device die and the second device die. Vias areformed to penetrate through the top portion of the gap-filling material.The vias are electrically coupled to the first device die and the seconddevice die. The method further includes forming redistribution linesover the gap-filling material using damascene processes, and formingelectrical connectors over and electrically coupling to theredistribution lines. The method of claim 1, wherein the filling the gapcomprises depositing an oxide. In an embodiment, the bonding the firstdevice die and the second device die to the substrate comprises fusionbonding. In an embodiment, the method includes forming a first pluralityof bond pads extending into the substrate, wherein the substrate is ablank semiconductor substrate; and forming a second plurality of bondpads extending into semiconductor substrates of the first device die andthe second device die, wherein the bonding further comprises bonding thefirst plurality of bond pads to the second plurality of bond padsthrough metal-to-metal direct bonding. In an embodiment, the forming theredistribution lines comprises forming a plurality of metal lines andvias interconnecting the first device die and the second device die. Inan embodiment, no polymer is formed between the substrate and theredistribution lines. In an embodiment, the method includes sawing thegap-filling material and the substrate into a same package. In anembodiment, both the first device die and the second device die are inthe same package. In an embodiment, the method includes forming amicro-channel in the substrate, wherein the micro-channel is configuredto conduct a coolant. In an embodiment, the forming the vias comprises:etching the gap-filling material and a passivation layer in the firstdevice die to form a via opening, wherein a top metal pad is exposed tothe via opening, and the top metal pad is in a low-k dielectric layer ofthe first device die; and filling the via opening with a conductivematerial.

In accordance with some embodiments of the present disclosure, a methodincludes attaching a first device die and a second device die to a heatspreader; filling a gap between the first device die and the seconddevice die with a dielectric material, wherein a top portion of thedielectric material covers the first device die and the second devicedie; forming vias penetrating through the top portion of the dielectricmaterial, wherein the vias are electrically coupled to the first devicedie and the second device die; forming a plurality of dielectric layersover the dielectric material; forming redistribution lines in theplurality of dielectric layers using dual damascene processes; formingelectrical connectors over and electrically coupling to theredistribution lines; and performing a die saw to cut through the heatspreader, the dielectric material, and the plurality of dielectriclayers to form a plurality of packages. In an embodiment, after the diesaw, the first device die and the second device die are in a samepackage in the plurality of packages. In an embodiment, theredistribution lines are fine-pitch RDLs having pitches smaller thanabout 0.8 μm. In an embodiment, the heat spreader comprises a glasssubstrate or a metal substrate, and the first device die and the seconddevice die are attached to the heat spreader through a thermal interfacematerial. In an embodiment, the heat spreader comprises a blank bulksilicon substrate, and the method further comprises: forming a firstplurality of bond pads extending into the blank bulk silicon substrate;and forming a second plurality of bond pads extending into semiconductorsubstrates of the first device die and the second device die, whereinthe attaching comprises a hybrid bonding.

In accordance with some embodiments of the present disclosure, a deviceincludes a blank substrate; a first device die and a second device diebonded to the blank substrate; a gap-filling material comprising: afirst portion filling a gap between the first device die and the seconddevice die; and a second portion covering the first device die and thesecond device die; vias penetrating through the second portion of thegap-filling material to electrically couple to the first device die andthe second device die; a plurality of dielectric layers over thegap-filling material; and a plurality of redistribution lines in theplurality of dielectric layers, wherein the plurality of redistributionlines comprises dual damascene structures. In an embodiment, the deviceincludes one of the dual damascene structures comprises: a via and ametal line over and continuously connected to the via, wherein the viaand the metal line in combination comprises: a diffusion barrier layerextending into both the via and the metal line; and a copper-containingmaterial over the diffusion barrier layer. In an embodiment, the devicefurther includes a first dielectric layer on a surface of the blanksubstrate; a second dielectric layer on a surface of the first devicedie, wherein the first dielectric layer is bonded to the seconddielectric layer through dielectric-to-dielectric bonding; a first metalpad in the first dielectric layer; and a second metal pad in the seconddielectric layer, wherein the first metal pad is bonded to the secondmetal pad through metal-to-metal bonding. In an embodiment, the deviceincludes the gap-filling material is an oxide. In an embodiment, thedevice includes no polymer exists between the blank substrate and theplurality of dielectric layers.

In accordance with some embodiments of the present disclosure, a deviceincludes a heat spreader; a first oxide layer over the heat spreader; afirst device die over and bonded to the heat spreader through the firstoxide layer; a dielectric gap-filling material encircling the firstdevice die; a plurality of low-k dielectric layers over the dielectricgap-filling material; a plurality of metal lines and vias in theplurality of low-k dielectric layers, wherein the plurality of metallines and vias are electrically connected to the first device die; and aplurality of solder regions over and electrically coupling to theplurality of metal lines and vias. In an embodiment, the device includesthe plurality of metal lines and vias comprise dual damascenestructures. In an embodiment, the device includes the dielectricgap-filling material further comprises a top portion overlapping thefirst device die, and the device further comprises a conductive viapenetrating through the top portion of the dielectric gap-fillingmaterial to electrically couple to the first device die. In anembodiment, the device further includes a second oxide layer over theheat spreader; and a second device die over and bonded to the heatspreader through the second oxide layer, wherein the plurality of metallines and vias electrically intercouples the first device die and thesecond device die. In an embodiment, the device further includes a thirdoxide layer on a surface of the first device die, wherein the thirdoxide layer is bonded to the first oxide layer. In an embodiment, thedevice further includes a first bond pad extending into the first oxidelayer; and a second bond pad extending into the third oxide layer,wherein the first bond pad is further bonded to the second bond pad. Inan embodiment, the device includes the first bond pad further extendsinto the heat spreader. In an embodiment, the device includes the firstdevice die comprises a semiconductor substrate, and the second bond padfurther extends into the semiconductor substrate. In an embodiment, thedevice includes each of the first bond pad and the second bond pad formsa grid.

In accordance with some embodiments of the present disclosure, a deviceincludes a heat spreader; a first device die and a second device dieover and attached to the heat spreader; a dielectric gap-fillingmaterial encapsulating the first device die and the second device dietherein; vias penetrating through the dielectric gap-filling material toelectrically couple to the first device die and the second device die; aplurality of redistribution lines over and electrically coupling to thevias, wherein the redistribution lines comprise dual damascenestructures; and a plurality of electrical connectors electricallycoupling to the plurality of redistribution lines. In an embodiment, thedevice includes the heat spreader comprises a semiconductor material. Inan embodiment, the device includes the first device die comprises asemiconductor substrate, and wherein the first device die is bonded tothe heat spreader through a metal pad, and the metal pad extends intothe semiconductor substrate of the first device die. In an embodiment,the device includes the heat spreader is formed of a metal. In anembodiment, the device includes the vias are in contact with aluminumpads of the first device die. In an embodiment, the device includes oneof the vias is in contact with a top metal pad of the first device die,and the top metal pad is in a low-k dielectric layer.

In accordance with some embodiments of the present disclosure, a methodincludes bonding a first device die and a second device die to a blanksubstrate; forming an oxide layer to fill a gap between the first devicedie and the second device die; forming redistribution lines over theoxide layer, wherein the first device die and the second device die areelectrically intercoupled through the redistribution lines; formingelectrical connectors over and electrically coupling to theredistribution lines; and sawing through the blank substrate and theoxide layer to form a plurality of packages, wherein the first devicedie and the second device die are in one of the plurality of packages.In an embodiment, the bonding comprises a fusion bonding. In anembodiment, the bonding further comprises metal-to-metal direct bonding.In an embodiment, the bonding is performed through a thermal interfacematerial. In an embodiment, the blank substrate is a semiconductorsubstrate, with no active device formed on the semiconductor substrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a blank substrate, whereinthe blank substrate is free from any device die extending into the blanksubstrate; a first dielectric layer on a surface of the blank substrate;a first metal pad in the first dielectric layer; and a first device dieand a second device die bonded to the blank substrate, wherein the firstdevice die comprises: a second dielectric layer at a surface of thefirst device die, wherein the first dielectric layer is bonded to thesecond dielectric layer through dielectric-to-dielectric bonding; and asecond metal pad in the second dielectric layer, wherein the first metalpad is bonded to the second metal pad through metal-to-metal bonding; agap-filling material comprising: a first portion filling a gap betweenthe first device die and the second device die; and a second portioncovering the first device die and the second device die; viaspenetrating through the second portion of the gap-filling material toelectrically couple to the first device die and the second device die; aplurality of dielectric layers over the gap-filling material; and aplurality of redistribution lines in the plurality of dielectric layers,wherein the plurality of redistribution lines comprises dual damascenestructures.
 2. The device of claim 1, wherein one of the dual damascenestructures comprises: a via and a metal line over and continuouslyconnected to the via, wherein the via and the metal line in combinationcomprises: a diffusion barrier layer extending into both the via and themetal line; and a copper-containing material over the diffusion barrierlayer.
 3. The device of claim 1, wherein the gap-filling material is anoxide.
 4. The device of claim 1, wherein no polymer exists between theblank substrate and the plurality of dielectric layers.
 5. The device ofclaim 1, wherein the first device die and the second device die are freefrom polymers.
 6. The device of claim 5, wherein no polymer is locatedbetween the blank substrate and the plurality of redistribution lines.7. A device comprising: a heat spreader; a first oxide layer over theheat spreader; a first bond pad extending into the first oxide layer;and a first device die over and bonded to the heat spreader through thefirst oxide layer, wherein the first device die comprises: a secondoxide layer at a surface of the first device die, wherein the secondoxide layer is bonded to the first oxide layer; and a second bond padextending into the second oxide layer, wherein the first bond pad isfurther bonded to the second bond pad; a dielectric gap-filling materialencircling the first device die; a plurality of low-k dielectric layersover the dielectric gap-filling material; a plurality of metal lines andvias in the plurality of low-k dielectric layers, wherein the pluralityof metal lines and vias are electrically connected to the first devicedie; and a plurality of solder regions over and electrically coupling tothe plurality of metal lines and vias.
 8. The device of claim 7, whereinthe plurality of metal lines and vias comprise dual damascenestructures.
 9. The device of claim 7, wherein the dielectric gap-fillingmaterial further comprises a top portion overlapping the first devicedie, and the device further comprises a conductive via penetratingthrough the top portion of the dielectric gap-filling material toelectrically couple to the first device die.
 10. The device of claim 7further comprising: a third oxide layer over the heat spreader; and asecond device die over and bonded to the heat spreader through the thirdoxide layer, wherein the plurality of metal lines and vias electricallyintercouples the first device die and the second device die.
 11. Thedevice of claim 7, wherein the first bond pad further extends into theheat spreader.
 12. The device of claim 7, wherein the first device diecomprises a semiconductor substrate, and the second bond pad furtherextends into the semiconductor substrate.
 13. The device of claim 7,wherein each of the first bond pad and the second bond pad is a part ofa plurality of bond pads that form a grid.
 14. The device of claim 7,wherein the first device die is free from any polymer layer therein. 15.A device comprising: a heat spreader; a first device die and a seconddevice die over and attached to the heat spreader, wherein the firstdevice die comprises a semiconductor substrate; a metal pad extendinginto the semiconductor substrate of the first device die, wherein themetal pad bonds the first device die to the heat spreader; a dielectricgap-filling material encapsulating the first device die and the seconddevice die therein; vias penetrating through the dielectric gap-fillingmaterial to electrically couple to the first device die and the seconddevice die; a plurality of redistribution lines over and electricallycoupling to the vias, wherein the redistribution lines comprise dualdamascene structures; and a plurality of electrical connectorselectrically coupling to the plurality of redistribution lines.
 16. Thedevice of claim 15, wherein the heat spreader comprises a semiconductormaterial.
 17. The device of claim 15, wherein the heat spreader isformed of a metal.
 18. The device of claim 15, wherein the vias are incontact with aluminum pads of the first device die.
 19. The device ofclaim 15, wherein one of the vias is in contact with a top metal pad ofthe first device die, and the top metal pad is in a low-k dielectriclayer.
 20. The device of claim 15, wherein the first device die furthercomprises a dielectric layer, and wherein the metal pad further extendsinto the dielectric layer.